Global Pass expiry; can I activate the pass within the 11 months but travel in the 12th month

Can you help, if I have a global 1month pass which expires on the 11 month from purchase and the date of expiry is 30th may if I activate to use on the 30th may do I get to use it for a month from that date? Or does my trips have to be completed by the 30th may? Hope that make sense.